Fix usage of collections.abc
Fix usage of collections.abc

Current logic to try importing the collections.abc module is broken and
the collections module is always imported, which results in deprecation
warning[1].

>>> import collections
>>> c_abc = collections.abc
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib64/python3.8/collections/__init__.py", line 55, in __getattr__
    raise AttributeError(f'module {__name__!r} has no attribute {name!r}')
AttributeError: module 'collections' has no attribute 'abc'

[1]
DeprecationWarning: Using or importing the ABCs from 'collections'
instead of from 'collections.abc' is deprecated since Python 3.3, and
in 3.10 it will stop working

Note that because Python 2 is no longer supported the logic to use
collcations is just removed.

Change-Id: Id0aeb77a68d556993bece14a71cdccc262c5461b

openstack/python-tripleoclient